78

PAINTING MATERIALS

Waxes. The composition of these substances is more varied than is that of
the oils and, at present, has been less investigated. Like most natural products,
they are mixtures of several components, and the isolation of these is a difficult
and lengthy task which has been attempted by comparatively few. The chief
proximate components are: (i) esters of the fatty acids with alcohols containing
a high number of carbon atoms; (2) free fatty acids; (3) free alcohols containing
a high number of carbon atoms; and (4) hydrocarbons. They can be divided as
animal, vegetable, bitumen, and mineral waxes. The following table gives the
chief analytical characteristics of the principal animal and vegetable waxes and
of montan wax. (For a discussion of the meaning of these characteristics, see
Oils and Fats.)
The waxes are esters of monohydric alcohols whereas oils are esters of a tri-
hydric alcohol The protective strength of most waxes against permeation of
moisture has given them an extensive use in the modern treatment of paintings,
though they are little used as a medium. Gettens and Bigelow, in a series of tests
of the moisture permeability of coatings, gave beeswax and ceresin a rating of 4
(average permeability in milligrams lost per day). Commercial mastic had a
rating of 35, dammar had 24, and the ratings for oils ran from 250 to 527. For
application over a normal and firm paint film with a thin film of varnish—thor-
oughly dry—Rosen (p. 115) recommends beeswax, I part, carnauba, 2 parts,
ceresin, 2 parts, as a surface coating for paintings. Wax adhesives have been
found to possess certain very decided advantages over the traditional glue mix-
ture as well as over synthetic materials for the purpose of lining canvases. Plender-
leith and Cursiter subjected a wax-lined painting, in which a well known recipe
was employed (equal parts of beeswax and resin with a small quantity of Venice
turpentine) as the cementing material, to a series of extreme tests of endurance,
and found that the wax proved remarkably unaffected by such drastic treatment.
Fink (' The Care and Treatment of Outdoor Bronze Statues/ Technical Studies,
II [1933], p. 34) has found paraffin to be the best protective coating which can
be applied to outdoor bronze statues. Wax has also proved itself suitable for
impregnating objects made of wood.
Waxes, Mstory in painting* The art of using colors prepared with wax began in
antiquity. The term, c encaustic,' which has long been applied to this method,
strictly means, * burning in/ an expression which is scarcely applicable to the mere
melting of wax colors. According to Pliny, the process was not originally restricted
to painting but included other processes in which melted wax was used. Lucas
(Ancient Egyptian Materials and Industries, pp. 280-281) says that the only wax
known to have been used in ancient Egypt was beeswax. It figured in mummifica-
tion, served as an adhesive, as a luting material on the covers of alabaster vases, as
a paint vehicle, as a fixing substance in the curls and plaits of wigs, and had a place
in the making of magical figures, in ship-building, and in other crafts. Eleven
specimens of beeswax from mummies examined by Lucas had melting points